This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-030873, filed Feb. 8, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to an electric motor pump with axial-flow impellers.
The electric motor pump of this type is known from U.S. Pat. No. 5,888,053, Jpn. Pat. Appln. KOKAI Publication No. 9-209976, Jpn. Pat. Appln. KOKAI Publication No. 8-177782, and Jpn. Pat. Appln. KOKAI Publication No. 58-8295.
An electric motor pump with axial-flow impellers comprises at least two axial-flow impellers, and an electric motor for rotating the axial-flow impellers. The electric motor further comprises an output shaft connected to the axial-flow impellers, radial bearings for rotatably supporting the output shaft, and a mechanism for rotating the output shaft. When the axial-impellers are driven for providing energy to a fluid in the electric motor pump, a thrust load is applied to the output shaft of the electric motor. This thrust load becomes larger with an increase in a discharge amount and/or a discharge pressure of the fluid. In order to receive this thrust load, a thrust bearing is required in addition to the radial bearings in the conventional electric motor. Furthermore, the thrust bearing becomes larger and more expensive with an increase in the discharge amount and/or the discharge pressure of the fluid.
The thrust bearing increases the weight and external size of the conventional electric motor pump described above, and raises its price as well.
The present invention has been contrived under the above circumstances, and an object of the present invention is to provide an electric motor pump with axial-flow impellers, which can omit the thrust bearing, can reduce the weight and external size as compared with the conventional electric motor pumps having axial-flow impellers, can decrease the noise generated therefrom, and does not shorten a life thereof.
In order to achieve the object of this invention described above, the electric motor pump with the axial-flow impellers, according to the present invention, comprises:
a pair of axial-flow impeller units;
an electric motor including an output shaft having both end portions connected to the pair of axial-flow impeller units, radial bearings for rotatably supporting the output shaft, and a mechanism for rotating the output shaft; and
a pair of pump housings provided on both sides of the electric motor in the longitudinal direction of the output shaft and including fluid inlet and outlet ports, the pump housings cooperating with the pair of the axial-flow impeller units to suck a fluid located around the electric motor pump into the housings through the inlet ports, move the sucked fluid in the longitudinal direction and discharge the fluid from the outlet ports, thereby mutually canceling thrust forces along the longitudinal direction applied to the output shaft by the axial-flow impeller units in the longitudinal direction.
In the electric motor pump with the axial-flow impellers according to the present invention which is constituted in the above described manner, when the pair of axial-flow impeller units are driven by the output shaft of the electric motor, the fluid located around the electric motor pump is moved in the longitudinal direction in the pair of pump housings provided on the both sides of the electric motor in the longitudinal direction of the output shaft. Then, the movements of the fluid along the longitudinal direction at the both end portions of the output shaft mutually cancel the thrust forces along the longitudinal direction applied to the output shaft by the pair of axial-flow impeller units. As a consequence, the electric motor pump with the axial-flow impellers according to the present invention does not require a thrust bearing for the output shaft in the electric motor.
Accordingly, in the electric motor pump with the axial-flow impellers according to the present invention, the weight and the external size thereof can be reduced as compared with those of the conventional one. Besides, its price can be made cheaper than that of the conventional one. In addition, a noise generated therefrom can be made smaller than that generated from the conventional one and the life of the pump can be prolonged.
In the electric motor pump with the axial-flow impellers according to the present invention which is constituted as described above, each of the pair of pump housings has a fluid outlet port at a location farther than the axial-flow impeller unit corresponding to each of the pump housings to the electric motor and at the same time a fluid inlet port at a location nearer than the corresponding axial-flow impeller unit to the electric motor. In this case, when each of the pair of axial-flow impeller units is rotated in a predetermined direction by the output shaft of the electric motor, the fluid is sucked through the fluid inlet port and is given with Kinetic energy so that the fluid is discharged from the outlet port.
In the case where the present invention is constituted in this manner, preferably each of the fluid outlet ports of the pair of pump housings is directed outward along the longitudinal direction of the end portion of the output shaft of the electric motor, the end portion corresponding to each of the pump housings, and each of the fluid inlet ports of the pair of pump housings is directed outward along the radial direction of the corresponding end portion of the output shaft of the electric motor.
With this constitution, the movements of the fluids along the longitudinal direction at the both end portions of the output shaft can make the structure of each of the pair of pump housings being simple for mutually canceling the thrust forces along the longitudinal direction applied to the output shaft by the pair of axial-flow impeller units.
Besides, each of the pair of pump housings has a plurality of fluid inlet ports, and preferably the fluid inlet ports are arranged on each of the pump housings at a predetermined interval in a circumferential direction of the end portion of the output shaft of the electric motor, the end portion corresponding to each of the pump housings.
With this structure described above, the fluid sucked into an inner space of each of the pair of the pump housings through each of the plurality of the fluid inlet ports can be activated to mutually cancel the forces applied to the output shaft via each of the pair of the axial-flow impeller units in the radial direction of the output shaft. Consequently, the strength of each of the radial bearings can be made smaller, the weight and the external size of the electric motor pump with the axial-flow impellers according to the present invention can be further reduced and the price thereof can be further made cheaper. In addition, the noise generated from the electric motor pump can be further reduced and the life thereof can be further prolonged.
In the electric motor pump with the axial-flow impellers according to the present invention which is constituted as described above, each of the pair of pump housings can have a fluid inlet port at a location farther than the axial-flow impeller unit corresponding to each of the pump housings to the electric motor and at the same time, each of the pump housings can have a fluid outlet port at a location nearer than the axial-flow impeller unit corresponding to each of the pump housings to the electric motor. In this case, when each of the pair of the axial-flow impeller units is rotated in a predetermined direction by the output shaft of the electric motor, the fluid is sucked through the inlet port into the inner space of each the pump housing and is given with Kinetic energy so that the fluid is discharged from the fluid outlet port.
When the electric motor pump of the present invention is constituted in this manner, it is preferable that the fluid inlet port of each of the pair of pump housings is directed outward along the longitudinal direction of each of the end portions of the output shaft of the electric motor, and the fluid outlet port of each of the pair of pump housings is directed outward along the radial direction of each of the end portions of the output shaft of the electric motor.
With this structure, the movements of the fluids along the longitudinal direction at both end portions of the output shaft can make the structure of each of the pair of pump housings being simple for mutually canceling thrust forces along the longitudinal direction applied to the output shaft by the pair of axial-flow impellers.
Furthermore, it is preferable that each of the pair of pump housings has a plurality of fluid outlet ports, and the plurality of fluid outlet ports are arranged on each of the pump housings at a predetermined interval in the circumferential direction of the end portion of the output shaft of the electric motor in each of the pair of pump housings.
With this structure, the fluid discharged from the inside space of each of the pair of pump housings through each of the plurality of fluid outlet ports can act so as to mutually cancel forces applied to the output shaft via the pair of axial-flow impeller units in the radial direction of the output shaft. Consequently, the strength of each of the radial bearings can be further reduced, and the weight and the external size of the electric motor pump with the axial-flow impellers can be reduced, and the price thereof can be further made cheaper. In addition, the noise generated from the electric motor pump can be further reduced, and the life thereof can be further prolonged.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.